Lubricity testing apparatus



June 9, 1964 c. w. YOUNG ETAL 3,136,150

LUBRICITY TESTING APPARATUS Filed Feb. 19, 1962 KLHW l W! .HH 1

INVENTORSI CHARLES W. YOUNG JOHN I. GATES BYI THEIR ATTORNEY creased wear and relatively United States Patent 3,136,150 LUBRICITY TESTING APPARATUS Charles W. Young, Los Angeies, and John 1. Gates, Pasadena, Calif., assiguors to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed Feb. 19, 1962, Ser. No. 174,680 9 Claims. (Cl. 73-10) The present invention is directed to an apparatus to determine the lubricity of muds under simulated drilling conditions. More particularly, the invention is directed to an apparatus to subject specimens of mud to varying temperatures, torsional forces and difierential pressures to determine the lubricity qualities of the mud.

When drilling a borehole with conventional rotary drilling apparatus, including a rotating drill string supplied with drilling mud under pressure, the string often sticks to the walls of the borehole. Sticking is objectionable because it makes both rotational and reciprocating movement of the string in the borehole diflicult or impossible. These difficulties result in 'loss of time, instrain on the drill string driving apparatus, as well as possible loss of the drill string and the hole.

It has been found that one of the prime causes of drill string sticking is the differential which exists between the high pressure inside of the column of mud adhering to the walls of the borehole and the relatively low ambient pressure of the permeable formation into which the borehole is being drilled. The differential is necessary in order to prevent fluid entrained in the formation from flowing into the borehole. As long as the drill string is concentric with the borehole and remains out of contact with thewalls thereof, no sticking problem occurs, since the drill string is subject to equal pressure on all sides. it is noted that during drilling with a drill-mud system the mud forms a column of filter cake on the permeable walls of the borehole which acts to effectively isolate high hydrostatic pressure of the mud within the borehole from the relatively low ambient pressure of the formation into which the borehole is drilled. The pressure differential between the interior of the borehole and the formation into which the borehole is drilled may cause sticking of the drill string when the string contacts the column of filter cake adhering to the walls of the borehole. Contact between the fitler cake and drill string may result from slight misalignment or bending'thereof, since drill strings are generally thousands of feet in length.

When the drill string contacts the mud cake on the side of the borehole, the contacted portion of the cake becomes isolated from the drilling mud under pressure in the borehole. The pressure in the isolated portion of the cake then generally drops to the ambient pressure of the formation in which the borehole is formed, and the drill string is held'a'gainst the wall of the borehole by the differential of pressure between the side of the, string exposed to drilling mud pressure and the side of the string exposed to formation pressure. The force holding the string against the borehole is equal to the product of the differential pressure times the area of contact between the string and borehole. When'it is attempted to move the string rotationally or axially within the borehole, it is necessary to overcome a force equaling the holding force due to differential pressure and the friction factor existing between the contacted mud cake and the drill string.

In order to reduce sticking due to the above discussed differential to a minimum, various devices have been attempted. For example, additives have been included in,

drilling mud compositions and drill strings have been subjected to mechanical forces and/ or electric currents.

The effect of additives with respect to the rate of build up of the mud cake and the rate at which pore'pressur'e within a contacted portion of mud cake becomes reduced 'ly between the legs 12 at the lower,

"ice

,muds.

Another object of the invention is to determine the lubricity of mudsunder conditions simulating those present in a borehole during drilling.

A further object of the invention rs to provide a lubricity testing apparatus wherein the variables present in a borehole may be accurately simulated and controlled.

Yet another object of the present invention is to provide an apparatus wherein the eifects of various factors on lubricity can be readily determined. I

These and other objects of the invention will become apparent from the following description and illustration of the invention.

In its broadest aspect, the apparatus of the present invention includes a closed hollow vessel, said vessel having a port open to relatively low pressure; a permeable sample receiving pallet disposed over said port; a plate disposed within said vessel and adapted to contact a sample on said sample receiving pallet; means operatively engaging said plate to impart rotation thereto and to indicate the amount of torque required for said rotation; and means to subject said vessel to high internal pressure with respect to the relatively low pressure to which the port is open.

Referring to the drawing, the single figure thereof represents an elevational view of the inventive apparatus with parts broken away to better illustrate interior details.

In the drawing, the numeral 10 designates the inventive apparatus in its entirety. The apparatus includes a stand 11 having spaced vertically extending legs 12. Platforms 13, 14 and 15 are secured to and extend transverseintermediate and upper sections thereof, respectively. Aslot 16 is formed through the platform 14 intermediate the connections of the legs 12 therewith. The slot 16 extends from the forward edge of the platform 14 to approximately the center thereof. A threaded opening 17 is formed through the platform 15 in approximate alignment with the end of the slot 16 at the approximate center of the platform 14.

A rod 21 having a support plate 22 adjustably'secured thereto is connected to the lower side of the platform 14. Support plate 22 is adapted to carry a sample receiving container, such as a measuring glass 23. i

A tank 24 having a threaded opening 25 in the lower surface thereof and a plug 26 in the side thereof is supported on the upper surface of the platform '14; A gasket of electrical insulating material 27 is interposed between the tank 24 and the platform 14. g

A vessel 28 having a chamber 31 therein is supported on the inner surface of the bottom of the tank 24. An annular gasket 32 is interposed between the tank 24 and the vessel 28 to insure sealed engagement therebetween. The vessel 28 includes a lower cap 33 having a bottom "34 and an upwardly extending cylindrical'section 35 with two slots 36 spaced from each other. Although only the forward slot 36 is illustrated, it is to be understood that an identical rearward slot is hidden from view. A spout 37 is threaded into an opening in the bottom 34 and into the opening 25 of the tank 24 and extends through the slot 16 of the platform'14. .Spout 37 includes a passage or port 38 extending between the chamber 31 and the atmosphere. An annular gasket 41 is disposed within the during testing.

upwardly extending section 35. A screen 42 extends over the upper surface of the bottom 34 and covers the port 38. The upper surface of the screen 42 is covered by a filter element 43'such as conventional filter paper, adapted to receive a mud cake 44. As illustrated, the screen 42 and filter element 43 form a permeable mud receiving pallet. It is noted that the pallet may include a more rigid filter element, such as core material or porous Alundum. In the latter case, the screen 42 may be omitted. V

The vessel 28 further includes a tubular section 45 received in the cylindrical section 35 of the lower cap 33. Two pins 46 are fixed to the lower part of the section 45 and extend radially outward therefrom. Pins 46 are spaced 180 from'each other and are adapted to engage slots 36 upon turning of the section 45 with respect to the cap 33, thereby forcing section 45 into engagement with the annular gasket 41.

An upper cap 47 having a recess 48 therein and a passage 51 therethrough, is received on the upper end of tubular section 45, An annular gasket 52 is disposed around the inner periphery of the recess 48 to establish a sealed connection between the section 45 and the cap 47. The cap 47 has a passage or port 53 extending therethrough between the chamber 31 and a conduit 54. The end of the conduit 54 remote from the cap 47 is connected to a tank 55 containing a fluid, such as gas, under pressure. A pressure control valve 56 is interposed between the ends of conduit 54. It is to be understood that other sources of fluid under pressure may be substituted for the tank 55 without departing from the invention.

A T-bolt 57 having an axial passage 58 therethrough is threaded into the opening 17. The lower end of the bolt 57 abuts against an annular gasket 61 resting in a recess in the cap 47 and is adapted to force said cap into sealing engagement with the section 45. A bolt 62 having a passage 63 in alignment with the passage 58 is threaded into the upper end of the T-bolt 57. An annular sealing elementor O-ring 64 is disposed between the bolts 57 and 62 to establish a seal between the passages in said bolts and a rod 65 passing through said passages.

The rod 65 extends slidably through the passages 63, 58 and 51 and into the chamber 31. A disc or plate 66 is affixed to the lower end of the rod 65 and is adapted to bear against the mud cake 44 disposed on the filter element 43. The upper end of the rod 65 extends through a bar 67 and is secured thereto by hex-bushings 68 and 69 fastened to the rod above and below the bar by set screws 72 and 73, respectively. Bar 67 has weights 74 secured to the opposite ends thereof to impart a downward force onto the rod 65 and, thereby, bias the disc 66 into bearing relationship with the cake 44. A torque imparting and indicating device, 75, such as a conventional torque .Wrench, engages the hex-bushing 69 and is adapted to impart rotational movement to the rod 65 through said bushing.

-; qwhenthe apparatus is in the assembled condition shown 'in the, illustration, the. tank 24 may be filled with a heat conductive medium such as oil 76. The oil may then be heated through use of a heater element 77 emersed therein. Temperature of the medium 76 is controlled through a thermometer 78, In order to maintain a constant controlled temperature in the medium 76 the heater element 77 and thermometer 78 may be coupled to a control mechanism as disclosed in United States Patent No. 2,838,- 644. A circulating impeller 81 extends into the medium 76 to insure that the temperature throughout the oil is uniform. Through this heating arrangement, the apparatus may be maintained at desired temperature levels It has been found that the process of electroendosmosis has potential use in the art of freeing metal surfaces stuck against surfaces of water bearing mud. In the use of the process, a source of direct electric current is connected across the metal and mud surfaces. The positive lead is applied to the mud and the negative lead is applied to the metal. Thus, a current is caused to flow through the mud, thereby drawing water from the mud towards the metal and the contacting surfaces of the mud and metal. The fluid on the surfaces acts as a lubricant and reduces the sticking forces therebetween. In order to test the effect of the electroendosmosis process, the rod is provided with a negative lead 82 and the tank 24 is provided with a positive lead 83. Through this arrangement the positive lead communicates with the mud cake 44 and the negative lead communicates with the metal plate 66. The gaskets 27, 61 and 64 act to insulate the plate 66 from the vessel 28.

In operation the tank 24, stand 11, lower cap 33 and tubular section 45 are assembled in the manner shown in the illustration, with the screen 42 and filter element 43 disposed within the cap 33. A specimen of mud is then introduced into the tubular section 45 and upper cap 47 is lowered into the illustrated position. During this time, the rod'65 and disc 66 are held in elevated position above the mud specimen in the tubular section 45. After the cap 47 is forced into sealing engagement with section 45 through downward tightening of the bolt 57, a gas is introduced into the chamber 31 from the tank 55. The pressure of'the gas within the chamber causes a portion of the fluid phase of the mud specimen to filtrate therethrough into the mud receiving pallet, thereby forming the mud cake 44, After the cake is formed, the disc 66 is lowered thereagainst and weights 74 are allowed to be supported by the rod 65, thereby biasing the disc into con tact with the cake 44. Upon the lapse of a desired time, the rod is turned through use of the device 75, and readings of the torque required to turn the rod and break the disc away from the mud cake are recorded. If temperature control of the test is desired, the tank 24 is filled with the medium 76. The heater element 77, thermometer 78 and impeller 81 are then activated to raise the temperature of the medium to the desired level.

In this manner, a mud specimen may be subjected to the variables present when a drill string rubs against a borehole, namely, a dilferential in fluid pressure, mechanical pressure, high temperature and torsional forces. Furthermore, each of these variables may be accurately controlled and recorded. It is to be understood that the weights 74 and the fluid pressure within the chamber 31 may be selectively varied.

From the foregoing description, it is believed apparent that the apparatus provides an inventive means for determining the eflect of various additives and lubricant facilitating means, such as electric current, on muds under simulated drilling conditions. The description is, however, merely intended to be explanatory of the invention. Van'- ous changes in the details of the illustrated construction may be made, within the scope of the appended claims, without departing from the spirit of the invention We claim as our invention:

1. A lubricity testing apparatus, comprising, a closed hollow vessel, said vessel having a port open to the exterior of the vessel; a permeable sample receiving pallet disposed over said port so as to isolate said port from the interior of said vessel; means to selectively subject the interior of the vessel to a high pressure relative to the exterior of the vessel to establish a differential in pressure across said pallet; a plate disposed within said vessel and adapted to contact a sample on said sample receiving pallet; means operatively engaging said plate to impart rotation thereto; and means to indicate the amount of torque requiredfor said rotation.

2. An apparatus according to claim 1 including means to bias the plate against a sample received on the pallet with preselected force.

3. An apparatus according to claim 1 including heating means to heat the vessel to preselected temperatures.

4. An'apparatus according to claim 1 wherein the vessel is electrically isolated from the plate andincluding means to subject a sample received on the pallet and contacted by the plate to the effects of electroendosmosis, said means comprising; a positive electrical lead in communication with the vessel and a negative electrical lead in communication with the plate.

5. A lubricity testing apparatus, comprising, a closed hollow vessel, said vessel having a port open to the exte/ rior of the vessel; a permeable sample receiving pallet disposed over said port so as to isolate said port from the interior of said vessel; means to selectively subject the interior of the vessel to a high pressure relative to the exterior of the vessel to establish a differential in pressure across said pallet; a rod sealingly extending into said vessel in slidable and rotatable engagement therewith, said rod having one end disposed inside of the vessel and another end disposed outside of said vessel; a plate fixed to said one end of the rod, said plate being adapted to contact a sample received on the sample receiving pallet; means operatively engaging said other end of the rod to impart rotation thereto; and means to indicate the amount of torque required for said rotation.

6. An apparatus according to claim 5 including a weight disposed on said other end of the rod, said weight being adapted to bias the plate into contact with a sample on the sample receiving pallet with a predetermined amount of force.

7. An apparatus according to claim 5 wherein the means to subject the vessel to high internal pressure comprises a source of fluid under pressure communicating with the interior of the vessel.

8. An apparatus according to claim 5 including heating means to heat the vessel to preselected temperatures.

9. An apparatus according to claim 5 wherein the vessel, plate and rod are fabricated of electrically conductive material and wherein the vessel is electrically isolated from the rod and plate and including means to subject a sample received on the pallet and contacted by the plate to the efiects of electroendosmosis, said means comprising; a positive electrical lead in communication with the vessel and a negative electrical lead in communication with the plate.

References Cited in the file of this patent UNITED STATES PATENTS 2,033,588 Pigott et al Mar. 10, 1936 FOREIGN PATENTS 964,352 Germany May 23, 1957 

1. A LUBRICITY TESTING APPARATUS, COMPRISING, A CLOSED HOLLOW VESSEL, SAID VESSEL HAVING A PORT OPEN TO THE EXTERIOR OF THE VESSEL; A PERMEABLE SAMPLE RECEIVING PALLET DISPOSED OVER SAID PORT SO AS TO ISOLATE SAID PORT FROM THE INTERIOR OF SAID VESSEL; MEANS TO SELECTIVELY SUBJECT THE INTERIOR OF THE VESSEL TO A HIGH PRESSURE RELATIVE TO THE EXTERIOR OF THE VESSEL TO ESTABLISH A DIFFERENTIAL IN PRESSURE ACROSS SAID PALLET; A PLATE DISPOSED WITHIN SAID VESSEL AND ADAPTED TO CONTACT A SAMPLE ON SAID SAMPLE RECEIVING PALLET; MEANS OPERATIVELY ENGAGING SAID PLATE TO IMPART ROTATION THERETO; AND MEANS TO INDICATE THE AMOUNT OF TORQUE REQUIRED FOR SAID ROTATION. 